This application claims priority from U.S. provisional application Ser. No. 60/535,866 filed Jan. 12, 2004.
Methods and compositions provide novel site-specific bioremediation for petroleum contamination of soil and groundwater.
Biological remediation techniques are used for some in-situ treatment of soils and groundwater contaminated with petroleum products. Bioremediation is the process of using microorganisms to naturally degrade contaminants into non-harmful elements, or elements that can be disposed of in accordance with regulatory criteria. The contaminants derived from a petroleum release are considered to be amenable to bioremediation. If the release is into the soil, petroleum-based contaminants, after being released into the soil, will migrate in several forms. The contaminants migrate downward by gravity toward the water table until the contaminants are trapped in pores as droplets, adsorb onto soil particles, dissolve in water, or reach an impermeable barrier.
In-situ bioremediation involves injecting a biomass, including microorganisms and associated nutrients, minerals and co-solvents, directly into the contaminated formation, either the soil contaminant plume, the groundwater contaminant plume, or both, in strategic locations determined based on geophysical site characteristics of the subsurface of the site. Due to the nature of the contaminated formation, the biomass, being in a slurry form, migrates laterally and vertically, depending on factors such as hydraulic conductivity, head pressure, and groundwater flow direction within the formation. After the slurry comes in contact with the contaminant, degradation begins.
The degradation of petroleum contaminants is achieved when ingredients of the slurry, plus nutrients from the environment, are transformed by the microorganisms into cell-building material and extra-cellular byproducts such as carbon dioxide and water.
The concentration of the individual indigenous microorganism strains and their relative percentages vary with the concentrations of pollutants in the soil and groundwater. The rate of biodegradation is proportional to the types and concentration of the bacteria available to do the work. Under normal conditions, the bacteria will double as frequently as every 15 to 20 minutes until they reach a population of several billion per gram of soil.
A site is suitable for bioremediation according to the industry if the petroleum contamination does not involve the required remediation of heavy metals, the contamination levels determined by analysis for Total Petroleum Hydrocarbons (TPH), are below 50,000 parts per million, the hydraulic conductivity of the site is greater than 10−7 centimeters per second (cm/sec), and the petroleum contamination results from fuel oil, diesel fuel, kerosene, or gasoline. Less refined petroleum products, such as lube oils or crude oil, are difficult to bioremediate. For a site where in-situ bioremediation appears to be a viable option, the first step is to perform a treatability study. (USEPA, 1995)
Although bioremediation is used in the art, costs need to be reduced. A source of high costs is considering more bacteria than are needed and not designing slurrys and injection systems that are site specific.